Currently, the Session Initiation Protocol (SIP) [RFC3261] does not define a standard way to monitor or record SIP calls. SIP does define a method for creating conference calls. Conference calls are designed for two-way communication (send/receive) between all devices on the conference call. However, conference calls are not designed for devices such as monitors/recorders that only need to receive and not transmit a media stream.
Conference call solutions require extensive processing in the network to mix all of the media streams. In addition to higher costs, other problems such as lost packets and dropped calls can result if network resources become overloaded. Moreover, it is difficult to un-mix a stream and monitor and/or record individual streams of a call.
Other solutions can monitor SIP calls based on existing SIP protocols. However, these solutions cannot provide full monitoring of media streams using standard SIP calls. For example, the system described in U.S. Patent Application No. 2007/0143858 describes a system that can provide third party surveillance by what is called a “partial wiretap”. This system can detect and record certain events such as the start of a SIP call, the end of a SIP call, and the duration of a SIP call. This system does not monitor individual media streams because the monitoring device is not set up to monitor the media streams of the SIP call. Therefore, this solution falls short of providing full call monitoring and recording.
Legacy systems such as described in U.S. Pat. No. 5,506,901 allow for monitoring of Time Division Multiplexed (TDM) streams of voice calls. However, this system is not designed to work using standard SIP messages and cannot be used to monitor a SIP call.
The problem with existing systems and standards is that they do not provide the ability to fully monitor and record a SIP call using standard SIP messages. Moreover, these systems do not provide the capability of monitoring and recording individual media streams of a SIP call.